An auto-focus method is subdivided into an active type that performs focusing by measuring a distance to a subject using an infrared ray and a passive type that employs a dedicated sensor (CCD/CMOD) configured to read a contrast of a subject.
The passive type auto-focus method uses a TTL (Through-The-Lens) contrast detection method. The contrast detection method continuously calculates the contrast of a part of an image (mainly the central portion) of an image while moving a lens, and determines that the image is in focus when the contrast is maximized. Meanwhile, in the case of the passive-type auto-focus method, a lens should be moved in an optical axis direction with respect to an image sensor in order to perform focusing.
An auto-focus camera module is equipped with an actuator for implementing auto-focus, and the actuator is generally designed and manufactured to constitute one assembly together with the lens module.
A method of coupling a lens module to a camera module may be subdivided into two methods. A first one is a method of coupling a thread type lens module using a screw to a camera module, and a second one is a method of coupling a screwless type lens module to a camera module.
The thread type coupling method refers to a method in which a male screw is formed on the lens module, a female screw is formed on a carrier that accommodates the lens module, and the lens module and the carrier are fastened to each other by rotary coupling of the male screw and the female screw. The screwless type coupling method refers to a method in which no threads are not designed on a lens module and a carrier, and the lens module and the carrier are fastened to each other by a combination of a cylinder and a ring-shaped structure.